U.S Pat. No. 4,891,058 relates to certain herbicidal 1-alkyl-3- aryl imidazolidine -2,4-diones that have the structural formula ##STR2## wherein R is lower alkyl, R.sup.1 is phenyl or substituted phenyl, X is alkyl, halo, haloalkyl or combinations thereof and N is the integer 0, 1, 2 or 3.